Fluid handling devices are becoming increasingly popular and there is an increased demand for fluid handling devices. One type of fluid handling device is a latching valve. Latching valves may be electrically-actuated or fluid-actuated, for example. Latching valves have a unique feature that allows the valve to remain in an opened and/or a closed state without requiring a continuous supply of power to the valve. For example, in electrically-actuated latching valves a solenoid may be provided and energizing the solenoid can actuate the valve. Often, a permanent magnet may be provided to latch or otherwise retain the valve in the actuated position absent energy being supplied to the solenoid. Although this system works adequately at first, the magnet is typically exposed to the fluid and thus, can easily corrode, thereby rendering the valve inoperable.
Another type of electrically-actuated latching valve is shown in U.S. Pat. No. 6,742,761, which is directed towards a shape memory alloy-actuated valve with a latching feature. Two actuating mechanisms consisting of shape memory alloy wires are used to actuate a plunger between an open and close state. A conical spring is used to hold the plunger in the actuated state in the absence of a biasing force by the shape memory alloy wires. Therefore, the '761 patent describes a shape memory alloy-actuated valve that includes a latching feature; however, the '761 valve requires an extra latching component, namely the conical spring to perform the latching feature. Therefore, although the valve shown in the '761 patent eliminates the problem associated with corroding magnets discussed above, the '761 patent requires an excessive number of parts that can be costly during manufacturing. Further, the conical spring is prone to damage during repeated actuations.
The above-mentioned approaches discuss electrically-actuated latching valves. Another type of latching valve comprises a fluid-actuated latching valve that uses one or more pilot valves. Fluid-actuated latching valves may be desirable in situations where the pressure and/or flow rate of the fluid would require an excessive amount of power if controlled directly. Although fluid-actuated latching valves are known, they typically rely upon solenoid controlled pilot valves, which as discussed above fail in some respects due to the power consumption required. Furthermore, in some situations, the electromagnetic field generated by the solenoid valve can present problems in certain environments. Additionally, solenoid valves often create an audible clicking noise as they are actuated that may be undesirable in certain situations. Further, pilot actuated valves typically require a separate pressurized fluid source, which can add to the complexity of the system.
Therefore, there exists a need in the art for a latching valve that can be fluid-actuated and use a minimum amount of power as it is actuated between positions. The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide a latching valve including pilot valves that are actuated using a shape memory alloy.